Methoxyaryl Surface Modifier and Organic Electronic Devices comprising such Methoxyaryl Surface Modifier

ABSTRACT

The present invention relates to a methoxyaryl surface modifier. In addition the present invention also relates to organic electronic devices comprising such methoxyaryl surface modifier.

TECHNICAL FIELD

The present invention relates to a methoxyaryl surface modifier. Inaddition the present invention also relates to organic electronicdevices comprising such methoxyaryl surface modifier.

BACKGROUND

Organic electronic devices, such as for example organic thin filmtransistors, organic photovoltaic cells or organic light emittingdevices, are substantially based on organic electronic materials, i.e.on materials being essentially carbon based. After intensive researchefforts, both in academia and industry, a significant number of organicmaterials with desirable properties have been identified, ranging fromsmall molecules to polymers.

However, for various reasons organic electronic devices are still mostlymade with metal (or metal oxide) electrodes. One of the challenges indesigning highly efficient organic electronic devices lies in matchingthe relative work functions of adjacent layers. While the properties oforganic electronic materials can be adapted by changing theircomposition, for example by introducing substituents or by polymerscomprising more than one monomer, such an adaptation is more difficultfor metal (or metal oxide) electrodes. Additionally, other factors suchas for example the adhesion between adjacent layers of an organicelectronic device may also have an effect on the overall performance ofsuch an organic electronic device.

In order to change the work function of metal (or metal oxide)electrodes, particularly of gold electrodes, and thus render them moreeasily compatible with organic electronic materials the metal (or metaloxide) electrodes may be covered with a self-assembled monolayer (SAM)of suitable molecules. For example, Boudinet et al. disclose in OrganicElectronics 11 (2010) 227-237 the modification of gold source and drainelectrodes with the following thiol compounds.

Self-assembled monolayers with stilbene-derivatives on gold have forexample been disclosed by M. Malicki et al. in Langmuir 2009, 25(14),7967-7975.

There is, however, still a need for further compounds that are suitablefor such self-assembled monolayers.

It is therefore an object of the present invention to provide compoundsthat are suitable for such self-assembled monolayers. Preferably suchcompounds would also allow modifying the work function of metal or metaloxide electrodes of organic electronic devices. Other objects of thepresent invention will become evident from the following description andexamples.

SUMMARY

The present inventors have now surprisingly found that the above objectsmay be attained either individually or in any combination by the presentself-assembled monolayer.

The present application therefore provides for a self-assembledmonolayer comprising a moiety of formula (I)

wherein R¹ is selected from the group consisting of methyl, ethyl,methyl wherein one or more hydrogen is substituted by fluorine and ethylwherein one or more hydrogen is substituted by fluorine; R² is —CH₂— or—CF₂—; Ar¹ is para-phenylene or a para-phenylene wherein one or morecarbon ring atom is substituted by N; X¹ is selected from the groupconsisting of —X^(a)—, —X^(a)—X^(b)—, —C(═X^(a))—X^(b)—, —X^(a)O₃—,—X^(a)—X^(b)O₃—, —PO₂H— and —PO₃H—, with X^(a) and X^(b) beingindependently of each S or Se; a is 2, 3, 4 or 5; b is 0, 1 or 2; c is0, 1 or 2; d is 0, 1 or 2; and e is 0, 1 or 2.

The present application also provides for metal or metal oxide surfacemodified by means of said self-assembled monolayer. Preferably saidmetal or metal oxide surface is an electrode.

Further, the present application provides for an organic electronicdevice comprising said self-assembled monolayer.

Furthermore, the present application also provides for a process forproducing such self-assembled monolayer and also such organic electronicdevice.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic exemplary representation of a top gate organicfield effect transistor.

FIG. 2 shows a schematic exemplary representation of a bottom gateorganic field effect transistor.

FIG. 3 is a schematic top view representation of the transistor ofExample 3.

FIG. 4 shows the transfer characteristics of the transistors of Example3.

FIG. 5 shows the transfer characteristics of the transistors of Example5.

DETAILED DESCRIPTION

For the purposes of the present application the term “self-assembledmonolayer” is used in a non-limiting way to denote a layer as definedherein. The term “self-assembled monolayer” is used to help distinguishthis layer from any other layer that might be mentioned in the presentapplication.

In general terms the present application provides for a self-assembledmonolayer comprising a moiety of general formula (I)

wherein R¹, R², Ar¹, X¹, a, b, c, d and e are as defined in thefollowing.

R¹ may be selected from the group consisting of methyl, ethyl, methylwherein one or more hydrogen is substituted by fluorine and ethylwherein one or more hydrogen is substituted by fluorine. Preferably R¹is methyl or methyl wherein one or more hydrogen is substituted byfluorine. Most preferably R¹ is methyl.

Examples of methyl wherein one or more hydrogen is substituted byfluorine may be selected from the group consisting of —CH₂F, —CHF₂ and—CF₃. Of these —CF₃ is preferred.

Examples of ethyl wherein one or more hydrogen is substituted byfluorine may be selected from the group consisting of —CH₂—CH₂F,—CH₂—CHF₂ and —CH₂—CF₃, —CHF—CH₃, —CHF—CH₂F, —CHF—CHF₂, —CHF—CF₃,—CF₂—CH₃, —CF₂—CH₂F, —CF₂—CHF₂ and —CF₂—CF₃. Of these —CH₂—CF₃,—CF₂—CH₃, —CF₂—CF₃ are preferred.

R² is —CH₂— or —CF₂—. Preferably R² is —CH₂—.

Ar¹ is para-phenylene or para-phenylene wherein one or more carbon ringatoms are substituted by N. Examples of suitable Ar¹ may be selectedfrom the group consisting of the following

which may be used in either direction, i.e. with either * in thedirection of the functional group X¹ of the moiety of formula (I). Ofthe above para-phenylene (II-1) is preferred. Optionally, one or more ofthe hydrogen present on Ar¹ may be replaced by fluorine.

Functional group X¹ is selected from the group consisting of —X^(a)—,—X^(a)—X^(b)—, —C(═X^(a))—X^(b)—, —X^(a)O₃—, —X^(a)—X^(b)O₃—, —PO₂H— and—PO₃H—, with X^(a) and X^(b) being independently of each other S or Se.Preferably X¹ is selected from the group consisting of —S—, —S—S—,—C(═S)—S—, —SO₃—, —S—SO₃—, —PO₂H— and —PO₃H—. Most preferably X¹ is —S—.

It is noted that with regards to functional group X¹ selected from thegroup consisting of —X^(a)O₃—, —X^(a)—X^(b)O₃—, —PO₂H— and —PO₃H— anumber of possible binding modes between X¹ and the metal or metal oxidesurface may be envisaged. Without wishing to be bound by theory it isbelieved that generally the bonding between these functional groups X¹and the metal or metal oxide surface is done by means of —O—. An exampleof such bonding is Metal-O—P—. These functional groups X¹ may forexample be bound to the metal or metal oxide surface by means of one ormore groups —O—. It is also possible that more than one such bindingmodes exist simultaneously.

Parameter a is 2, 3, 4 or 5. Preferably a is 2 or 3. Most preferably ais 3.

Parameter b is 0, 1 or 2. Preferably b is 0 or 1.

Parameter c is 0, 1, or 2. Preferably c is 0 or 1.

Parameter d is 0, 1, or 2. Preferably d is 0 or 1.

Parameter e is 0, 1, or 2. Preferably e is 0 or 1.

Preferably at least one of parameters b, c, d and e is 1, i.e.b+c+d+e≧1.

Preferred combinations of b, c, d and e may be selected from thefollowing:

(i) b+d is 1; preferably b is 1 and d is 0.

(ii) b, c and e are all 1; and d is 0.

(iii) e is 1; and b, c and d are all 0.

(iv) b, c, d and e are all 1.

(v) c and e are all 1; and b and d are all 0.

(vi) c is 1; and b, d and e are all 0.

Suitable examples of moieties of formula (I) may be selected from thefollowing formulae (I-1) to (I-11)

The present self-assembled monolayer may also comprise more than onemoiety of the present invention or may also comprise a compound known toform self-assembled monolayers, such as the compounds disclosed byBoudinet et al. in Organic Electronics 11 (2010) 227-237 or by M.Malicki et al. in Langmuir 2009, 25(14), 7967-7975.

Preferably the self-assembled monolayers of the present invention mayhave a thickness (measured perpendicular to the surface of such layer)from 1 to 10, more preferably from 1 to 5, even more preferably from 1to 3, and still even more preferably from 1 to 2 molecular layers. Mostpreferably said thickness is one molecular layer.

The resulting self-assembled monolayers have been found useful for themodification of surface properties of metal or metal oxide surfaces.Such metal or metal oxide surfaces may for example be electrodes inelectronic devices. Specific examples of such electrodes in electronicdevices may for example be the source and drain electrodes in an organicfield effect transistor.

The types of metal and metal oxide that may be used in the presentinvention are not particularly limited and may also include alloys andany blend of metals, any blend of metal oxides as well as any blend ofmetals and metal oxides.

Exemplary metals, which are particularly suitable as electrodes inelectronic devices, particularly in organic electronic devices, may beselected from the group consisting of gold, silver, copper, aluminum,nickel, palladium, platinum, titanium and any blend thereof. Of thesegold and silver are particularly preferred. Silver is most preferred.

Exemplary alloys, which are particularly suitable as electrodes inelectronic devices, particularly in organic electronic devices, includestainless steel (e.g., 332 stainless steel, 316 stainless steel), alloysof gold, alloys of silver, alloys of copper, alloys of aluminum, alloysof nickel, alloys of palladium, alloys of platinum, and alloys oftitanium.

Exemplary electrically conducting metal oxides include indium tin oxide,fluorinated tin oxide, tin oxide, zinc oxide and any blend thereof.

Thus, the present application also relates to metal or metal oxidesurfaces covered by a self-assembled monolayer comprising a moiety ofthe present invention. The term “covered” is to mean that at least 10%,or 20% or 30%, or 40%, or 50%, or 60%, or 70% or 80% or 90% or 95% or97% or 99% of such metal or metal oxide surface is covered by saidself-assembled monolayer. In other words, the metal or metal oxidesurface is in contact with said self-assembled monolayer. Preferablysaid contact is a direct physical contact. Expressed differently, it ispreferred that the present self-assembled monolayer is directly adjacentto the metal or metal oxide surface.

For the purposes of the present application the term “metal” may alsodenote a blend of one or more metals and one or more metal oxideswherein the content of the one or more metals is more than 50 wt %,relative to the total weight of said blend. Analogously the term “metaloxide” may also denote a blend of one or more metals and one or moremetal oxides wherein the content of the one or more metal oxides is morethan 50 wt %, relative to the total weight of said blend.

Without wishing to be bound by theory it is believed that the moietiesof general formula (I), which are comprised in said self-assembledmonolayer, are oriented in such a way that functional group X¹ is inproximity of the metal or metal oxide surface while themethoxyaryl-group faces away from the metal or metal oxide surface. Itis believed that such orientation of the moieties of the presentinvention in such a self-assembled monolayer results in improved surfaceproperties, such as improved charge injection and charge transport, onthe side of the methoxyaryl-groups. Furthermore, the number and type ofthe R¹O-groups on the methoxyaryl-groups allows controlling thewettability of such self-assembled monolayer and thus help in thedeposition of further layers thereon.

Furthermore, the present application also relates to electronic devices,preferably to organic electronic devices, comprising a metal or metaloxide surface covered by said self-assembled monolayer of the presentinvention. For example, the present application relates to electronicdevices, preferably to organic electronic devices, comprising a metal ormetal oxide electrode covered by a self-assembled monolayer of thepresent invention.

The electronic devices of the present invention may for example beselected from the group consisting of organic field effect transistors(OFET), thin film transistors (TFT), integrated circuits (IC), logiccircuits, capacitors, radio frequency identification (RFID) tags,devices or components, organic light emitting diodes (OLED), organiclight emitting transistors (OLET), flat panel displays, backlights ofdisplays, organic photovoltaic devices (OPV), organic solar cells (OSC),photodiodes, laser diodes, photoconductors, organic photodetectors(OPD), electrophotographic devices, electrophotographic recordingdevices, organic memory devices, sensor devices, biosensors, biochips,security markings, security devices, and components or devices fordetecting and discriminating DNA sequences.

Preferably said electronic devices are selected from the groupconsisting of organic field effect transistors (OFET), organic thin filmtransistors (OTFT), organic light emitting diodes (OLED), organic lightemitting transistors (OLET), organic photovoltaic devices (OPV), organicphotodetectors (OPD), organic solar cells, laser diodes, Schottkydiodes, photoconductors and photodetectors.

Such electronic devices are well known to the skilled person and will inthe following be illustrated using organic field effect transistors(OFETs). An organic field effect transistor may comprise a gateelectrode, an insulating (or gate insulator) layer, a source electrode,a drain electrode and an organic semiconducting channel connecting thesource and drain electrodes, wherein any or all of the electrodes—ifcomprising a metal or a metal oxide or both—may be in contact with aself-assembled monolayer in accordance with the present invention. Otherfeatures of the OFET are well known to those skilled in the art.

OFETs where an organic semiconducting material is arranged as a thinfilm between a gate dielectric and a drain and a source electrode, aregenerally known and are described for example in U.S. Pat. No.5,892,244, U.S. Pat. No. 5,998,804 and U.S. Pat. No. 6,723,394.

In an OFET device gate, source and drain electrodes and an insulatinglayer and a semiconducting layer may be arranged in any sequence,provided that the source electrode and the drain electrode are separatedfrom the gate electrode by the insulating layer, the gate electrode andthe semiconductor layer both contact the insulating layer, and thesource electrode and the drain electrode both contact the semiconductinglayer.

An OFET device according to the present invention preferably comprises:

-   -   a source electrode,    -   a drain electrode,    -   a gate electrode,    -   a self-assembled monolayer in accordance with the present        invention,    -   a semiconducting layer,    -   one or more gate insulator layers, and    -   optionally a substrate,

wherein at least one of the electrodes comprises a metal or a metaloxide. Preferably said at least one of the electrodes comprising a metalor a metal oxide is covered by the self-assembled monolayer.

The OFET device can be a top gate device or a bottom gate device.Suitable structures and manufacturing methods of an OFET device areknown to the skilled person and are described in the literature, forexample in US 2007/0102696 A1.

FIG. 1 shows a schematic representation of a typical top gate OFETaccording to the present invention, including source (S) and drain (D)electrodes (2) provided on a substrate (1), a self-assembled monolayer(3) of a moiety of general formula (I) of the present invention providedon the S/D electrodes, a layer of organic semiconducting material (4)provided on the S/D electrodes and the self-assembled monolayer (3), alayer of dielectric material (5) as gate insulator layer provided on theorganic semiconducting layer (4), a gate electrode (6) provided on thegate insulator layer (5), and an optional passivation or protectionlayer (7) provided on the gate electrode (6) to shield it from furtherlayers or devices that may be provided later or to protect it fromenvironmental influence. The area between the source and drainelectrodes (2), indicated by the double arrow, is the channel area.

FIG. 2 shows a schematic representation of a typical bottom gate-bottomcontact OFET according to the present invention, including a gateelectrode (6) provided on a substrate (1), a layer of dielectricmaterial (5) (gate insulator layer) provided on the gate electrode (4),source (S) and drain (D) electrodes (2) provided on the gate insulatorlayer (6), a self-assembled monolayer (3) of a moiety of general formula(I) of the present invention provided on the S/D electrodes, a layer ofan organic semiconducting material (4) provided on the S/D electrodesand the self-assembled monolayer (3), and an optional protection orpassivation layer (7) provided on the organic semiconducting layer (4)to shield it from further layers or devices that may be later providedor protect it from environmental influences.

Preferably the gate insulator layer is deposited, e.g. by spin-coating,doctor blading, wire bar coating, spray or dip coating or other knownmethods, from a formulation comprising an insulator material and one ormore solvents with one or more fluoro atoms (fluorosolvents), preferablya perfluorosolvent. A suitable perfluorosolvent is e.g. FC75® (availablefrom Acros, catalogue number 12380). Other suitable fluoropolymers andfluorosolvents are known in prior art, like for example theperfluoropolymers Teflon AF® 1600 or 2400 (from DuPont) or Fluoropel®(from Cytonix) or the perfluorosolvent FC 43® (Acros, No. 12377).Especially preferred are organic dielectric materials having adielectric constant from 1.0 to 5.0, very preferably from 1.8 to 4.0(“low k materials”), as disclosed for example in US 2007/0102696 A1 orU.S. Pat. No. 7,095,044.

In security applications, OFETs and other devices with semiconductingmaterials according to the present invention, like transistors ordiodes, can be used for RFID tags or security markings to authenticateand prevent counterfeiting of documents of value like banknotes, creditcards or ID cards, national ID documents, licenses or any product withmonetary value, like stamps, tickets, shares, cheques etc.

Alternatively, the electronic device in accordance with the presentinvention may be an OLED. Common OLEDs are realized using multilayerstructures. An emission layer is generally sandwiched between one ormore electron-transport and/or hole-transport layers. By applying anelectric voltage electrons and holes as charge carriers move towards theemission layer where their recombination leads to the excitation andhence luminescence of the lumophor units contained in the emissionlayer. The selection, characterization as well as the processing ofsuitable monomeric, oligomeric and polymeric compounds or materials forthe use in OLEDs is generally known by a person skilled in the art, see,e.g., Müller et al, Synth. Metals, 2000, 111-112, 31-34, Alcala, J.Appl. Phys., 2000, 88, 7124-7128 and the literature cited therein.

According to another use, the materials according to this invention,especially those showing photoluminescent properties, may be employed asmaterials of light sources, e.g. in display devices, as described in EP0 889 350 A1 or by C. Weder et al., Science, 1998, 279, 835-837.

The electronic devices of the present invention may be produced bystandard methods well known to the skilled person. Liquid coating ofdevices is more desirable than vacuum deposition techniques. Solutiondeposition methods are especially preferred. Preferred depositiontechniques include, without limitation, dip coating, spin coating, inkjet printing, nozzle printing, letter-press printing, screen printing,gravure printing, doctor blade coating, roller printing, reverse-rollerprinting, offset lithography printing, dry offset lithography printing,flexographic printing, web printing, spray coating, curtain coating,brush coating, slot dye coating or pad printing.

The organic semiconducting materials and methods for applying theorganic semiconductor layer can be selected from standard materials andmethods known to the person skilled in the art, and are described in theliterature.

The organic semiconducting material may for example be an n-type orp-type organic semiconductor, which can be deposited by vacuum or vapordeposition, or preferably deposited from a solution. Preferably organicsemiconducting materials are used which have a FET mobility of greaterthan 10⁻⁵ cm²V⁻¹s⁻¹.

The organic semiconducting materials are for example used as the activechannel material in an organic field effect transistor or a layerelement of an organic rectifying diode. Organic semiconducting materialsthat may be deposited by liquid coating to allow ambient processing arepreferred. Organic semiconducting materials are preferably spray-, dip-,web- or spin-coated or deposited by any liquid coating technique.Ink-jet deposition is also suitable. The organic semiconducting materialmay optionally be vacuum or vapor deposited.

The semiconducting channel may also be a composite of two or more of thesame types of semiconductors. Furthermore, a p-type channel material mayfor example be mixed with n-type materials for the effect of doping thelayer. Multilayer semiconductor layers may also be used. For example thesemiconductor may be intrinsic near the insulator interface and a highlydoped region can additionally be coated next to the intrinsic layer.

The organic semiconducting material may be a monomeric compound (alsoreferred to as “small molecule”, as compared to a polymer ormacromolecule) or a polymeric compound, or a mixture, dispersion orblend containing one or more compounds selected from either or both ofmonomeric and polymeric compounds.

In case of monomeric materials, the organic semiconducting material ispreferably a conjugated aromatic molecule, and contains preferably atleast three aromatic rings. Preferred monomeric organic semiconductingmaterials are selected from the group consisting of conjugated aromaticmolecules containing 5-, 6- or 7-membered aromatic rings, morepreferably containing 5- or 6-membered aromatic rings.

In these conjugated aromatic molecules, each of the aromatic ringsoptionally contains one or more hetero atoms selected from Se, Te, P,Si, B, As, N, O or S, preferably from N, O or S. Additionally oralternatively, in these conjugated aromatic molecules, each of thearomatic rings is optionally substituted with alkyl, alkoxy, polyalkoxy,thioalkyl, acyl, aryl or substituted aryl groups, halogen, particularlyfluorine, cyano, nitro or an optionally substituted secondary ortertiary alkylamine or arylamine represented by —N(R′)(R″), where R′ andR″ are independently of each other selected from the group consisting ofH, an optionally substituted alkyl group, or an optionally substitutedaryl, alkoxy or polyalkoxy group. Where R′ and R″ is an alkyl or arylgroup, these are optionally fluorinated.

In these conjugated aromatic molecules, the aromatic rings areoptionally fused or are optionally linked to each other by a conjugatedlinking group such as —C(T¹)═C(T²)—, —C≡C—, —N(R′″)—, —N═N—, —C(R′″)═N—,—N═C(R′″)—, wherein T¹ and T² are independently of each other selectedfrom the group consisting of H, Cl, F, —CN or a C₁-C₁₀ alkyl group,preferably a C₁-C₄ alkyl group; R′″ is selected from the groupconsisting of H, an optionally substituted C₁-C₂₀ alkyl group or anoptionally substituted C₄-C₃₀ aryl group. Where R′″ is an alkyl or arylgroup, these may optionally be fluorinated.

Further preferred organic semiconducting materials that can be used inthis invention include compounds, oligomers and derivatives of compoundsselected from the group consisting of conjugated hydrocarbon polymerssuch as polyacene, polyphenylene, poly(phenylene vinylene), polyfluoreneincluding oligomers of those conjugated hydrocarbon polymers; condensedaromatic hydrocarbons such as tetracene, chrysene, pentacene, pyrene,perylene, coronene, or soluble, substituted derivatives of these;oligomeric para substituted phenylenes such as p-quaterphenyl (p-4P),p-quinquephenyl (p-5P), p-sexiphenyl (p-6P), or soluble substitutedderivatives of these; conjugated heterocyclic polymers such aspoly(3-substituted thiophene), poly(3,4-bisubstituted thiophene),optionally substituted polythieno[2,3-b]thiophene, optionallysubstituted polythieno[3,2-b]thiophene, poly(3-substituted selenophene),polybenzothiophene, polyisothianapthene, poly(N-substituted pyrrole),poly(3-substituted pyrrole), poly(3,4-bisubstituted pyrrole), polyfuran,polypyridine, poly-1,3,4-oxadiazoles, polyisothianaphthene,poly(N-substituted aniline), poly(2-substituted aniline),poly(3-substituted aniline), poly(2,3-bisubstituted aniline),polyazulene, polypyrene; pyrazoline compounds; polyselenophene;polybenzofuran; polyindole; polypyridazine; benzidine compounds;stilbene compounds; triazines; substituted metallo- or metal-freeporphines, phthalocyanines, fluorophthalocyanines, naphthalocyanines orfluoronaphthalocyanines; C₆₀ and C₇₀ fullerenes; N,N′-dialkyl,substituted dialkyl, diaryl or substituteddiaryl-1,4,5,8-naphthalenetetracarboxylic diimide and fluoroderivatives; N,N′-dialkyl, substituted dialkyl, diaryl or substituteddiaryl 3,4,9,10-perylenetetracarboxylicdiimide; bathophenanthroline;diphenoquinones; 1,3,4-oxadiazoles;11,11,12,12-tetracyanonaptho-2,6-quinodimethane; α, α′bis(dithieno[3,2-b2′,3′-d]thiophene); 2,8-dialkyl, substituted dialkyl,diaryl or dialkynyl anthradithiophene;2,2′-bibenzo[1,2-b:4,5-b′]dithiophene. Preferred compounds are thosefrom the above list and derivatives thereof which are soluble in organicsolvents.

Especially preferred organic semiconducting materials are selected fromthe group consisting of polymers and copolymers comprising one or morerepeating units selected from thiophene-2,5-diyl, 3-substitutedthiophene-2,5-diyl, selenophene-2,5-diyl, 3-substitutedselenophene-2,5-diyl, optionally substitutedthieno[2,3-b]thiophene-2,5-diyl, optionally substitutedthieno[3,2-b]thiophene-2,5-diyl, optionally substituted2,2′-bithiophene-5,5′-diyl, optionally substituted2,2′-biselenophene-5,5′-diyl.

Further preferred organic semiconducting materials are selected from thegroup consisting of substituted oligoacenes such as pentacene, tetraceneor anthracene, or heterocyclic derivatives thereof, like6,13-bis(trialkylsilylethynyl) pentacenes or5,11-bis(trialkylsilylethynyl) anthradithiophenes, as disclosed forexample in U.S. Pat. No. 6,690,029, WO 2005/055248 A1 or U.S. Pat. No.7,385,221.

In another preferred embodiment of the present invention the organicsemiconducting layer of the electronic device comprises one or moreorganic binders to adjust the rheological properties as described forexample in WO 2005/055248 A1, in particular an organic binder which hasa low permittivity, E, at 1,000 Hz of 3.3 or less.

The binder is selected for example from poly(alpha-methylstyrene),polyvinylcinnamate, poly(4-vinylbiphenyl) or poly(4-methylstyrene, orblends thereof. The binder may also be a semiconducting binder selectedfor example from polyarylamines, polyfluorenes, polythiophenes,polyspirobifluorenes, substituted polyvinylenephenylenes, polycarbazolesor polystilbenes, or copolymers thereof.

A preferred dielectric material for use in the present inventionpreferably comprises a material with a low permittivity of between 1.5and 3.3 at 1000 Hz. An example of such a material is Cytop™ 809Mcommercially available from Asahi Glass.

The transistor device according to the present invention may also be acomplementary organic thin film transistor (CTFT) comprising both ap-type semiconducting channel and an n-type semiconducting channel.

The self-assembled monolayer of the present invention are not onlyuseful in organic field effect transistors, but can also be used in anyorganic electronic device comprising a metal electrode or a metal oxideelectrode, like for example organic light emitting devices (OLEDs) ororganic photovoltaic (OPV) devices. The skilled person can easily makethe required modifications in order to use it in other organicelectronic devices.

For example, the present can also be applied to an electrode in anorganic photovoltaic device, like for example in a bulk heterojunction(BHJ) solar cell. The organic photovoltaic device can be of any typeknown from the literature [see e.g. Waldauf et al., Appl. Phys. Lett.89, 233517 (2006)].

A preferred organic photovoltaic device according to the presentinvention comprises:

-   -   a low work function electrode (for example a metal, such as        aluminum), and a high work function electrode (for example        indium tin oxide, frequently referred to as “ITO”), one of which        is transparent,    -   a layer (also referred to as “active layer”) comprising a hole        transporting material and an electron transporting material,        preferably selected from organic semiconducting materials,        situated between the low work function electrode and the high        work function electrode; the active layer can exist for example        as a bilayer or two distinct layers or blend or mixture of        p-type and n-type semiconductor, forming a bulk heterjunction        (BHJ) (see for example Coakley, K. M. and McGehee, M. D. Chem.        Mater. 2004, 16, 4533),    -   an optional coating (for example of LiF) on the side of the low        work function electrode facing the active layer, to provide an        ohmic contact for electrons,

wherein at least one of the electrodes, preferably the high workfunction electrode, is covered with a self-assembled monolayer inaccordance with the present invention.

Another preferred organic photovoltaic device according to the presentinvention is an inverted organic photovoltaic device that comprises:

-   -   a low work function electrode (for example a metal, such as        gold), and a high work function electrode (for example ITO), one        of which is transparent,    -   a layer (also referred to as “active layer”) comprising a hole        transporting material and an electron transporting material,        preferably selected from organic semiconducting materials,        situated between the low work function electrode and the high        work function electrode; the active layer can exist for example        as a bilayer or two distinct layers or blend or mixture of        p-type and n-type semiconductor, forming a BHJ,    -   an optional coating (for example of TiO_(x)) on the side of the        high work function electrode facing the active layer, to provide        an ohmic contact for holes,

wherein at least one of the electrodes, preferably the high workfunction electrode, is covered with a self-assembled monolayer inaccordance with the present invention.

Thus, in the organic photovoltaic devices of the present inventionpreferably at least one of the electrodes, preferably the high workfunction electrode, is covered, on its surface facing the active layer,by a layer comprising a moiety in accordance with the present invention.Said layer is advantageously applied by process according to the presentinvention as described above and below.

The organic photovoltaic devices in accordance with the present inventinvention typically comprise a p-type (electron donor) semiconductor andan n-type (electron acceptor) semiconductor. The p-type semiconductor isfor example a polymer like poly(3-alkyl-thiophene) (P3AT), preferablypoly(3-hexylthiophene) (P3HT), or alternatively another selected fromthe groups of preferred polymeric and monomeric organic semiconductingmaterial as listed above. The n-type semiconductor can be an inorganicmaterial such as zinc oxide or cadmium selenide, or an organic materialsuch as a fullerene derivate, for example (6,6)-phenyl-butyric acidmethyl ester derivatized methano C₆₀ fullerene, also known as “PCBM” or“C₆₀PCBM”, as disclosed for example in G. Yu, J. Gao, J. C. Hummelen, F.Wudl, A. J. Heeger, Science 1995, Vol. 270, p. 1789 ff and having thestructure shown below, or an structural analogous compound with e.g. aC₇₀ fullerene group (C₇₀PCBM), or a polymer (see for example Coakley, K.M. and McGehee, M. D. Chem. Mater. 2004, 16, 4533).

A preferred material of this type is a blend or mixture of a polymerlike P3HT or another polymer selected from the groups listed above, witha C₆₀ or C₇₀ fullerene or modified fullerene like PCBM. Preferably theratio polymer:fullerene is from 2:1 to 1:2 by weight, more preferablyfrom 1.2:1 to 1:1.2 by weight, most preferably 1:1 by weight. For theblended mixture, an optional annealing step may be necessary to optimizeblend morphology and consequently organic photovoltaic deviceperformance.

The present self-assembled monolayer may be prepared by applying acompound (in the following denoted “precursor compound”) comprising themoiety of formula (I) to a metal or metal oxide surface, which issupported on a substrate. Preferably said precursor compound is ofgeneral formula (I′) or (I″)

wherein the moiety of formula (I) is as defined above.

The process of the present invention therefore provides for a processfor the preparation of a self-assembled monolayer on a metal surface ora metal oxide surface, and ultimately the production of electronicdevices, preferably organic electronic devices, comprising suchself-assembled monolayer, said process comprising the steps of

-   (a) providing a metal surface or a metal oxide surface, and-   (c) applying one or more precursor compounds of formulae (I′) or    (I″) as defined above to said metal surface or metal oxide surface,

thus obtaining a self-assembled monolayer in accordance with the presentinvention on said metal surface or metal oxide surface.

The metal surface or the metal oxide surface of step (a) may be thesurface of an electrode. In a organic field effect transistor saidelectrode may for example be the source electrode or the drain electrodeor both. Preferably, such electrodes are provided on a supporting layer.Examples of suitable supporting layers or substrates, as they may bereferred to in the context of electronic devices, are given below.

The precursor compound of formula (I′) or (I″) as defined above may beapplied onto the metal surface or the metal oxide surface by vacuum orvapor deposition methods or by liquid coating methods. Exemplarydeposition methods include physical vapor deposition (PVD), chemicalvapor deposition (CVD), sublimation or liquid coating methods. Liquidcoating methods are preferred. Particularly preferred are solvent-basedliquid coating methods.

In solvent-based liquid coating a formulation, which comprises aprecursor compound of formula (I′) or (I″) as defined above and asolvent, is deposited onto the metal surface or the metal oxide surface.Optionally, following deposition the solvent may be at least partiallyevaporated. Preferred solvent-based liquid coating methods include,without limitation, dip coating, spin coating, ink jet printing,letter-press printing, screen printing, doctor blade coating, rollerprinting, reverse-roller printing, offset lithography printing,flexographic printing, gravure printing, web printing, spray coating,brush coating and pad printing.

In the following, the step of applying the precursor compound of formula(I′) or (I″) as defined above to an electrode so as to obtain theself-assembled monolayer of the present invention may also be referredto as “SAM treatment”.

Suitable solvents for use in the step (a) of the above process may beselected from the group consisting of alcohols, ethers, ketones,aromatic hydrocarbons and any mixture of any of these. Suitable alcoholsmay for example be selected from the group consisting of methanol,ethanol, iso-propanol and n-propanol. Suitable ethers may have a linearor a cyclic structure and may for example be selected from the groupconsisting of diethylether, tetrahydrofuran (THF), butyl phenyl ether,methyl ethyl ether and 4-methylanisole. Suitable ketones may for examplebe selected from the group consisting of acetone, 2-heptanone andcyclohexanone. Suitable aromatic hydrocarbons may for example beselected from the group consisting of toluene, mesitylene, o-xylene,m-xylene, p-xylene, cyclohexylbenzene and halogenated aromatichydrocarbons. Examples of such halogenated aromatic hydrocarbons arechlorobenzene, dichlorobenzene and trichlorobenzene as well as anymixture of any of these.

Preferably the precursor compounds of formula (I′) or (I″) are presentin the formulation or solution in from 0.01 wt % to 10 wt %, preferablyfrom 0.01 wt % to 5 wt %, and most preferably from 0.05 wt % to 2 wt %,with wt % being relative to the total weight of the formulation orsolution.

The metal or metal oxide may be applied to the substrate by any of theconventional methods. The methods may for example be selected fromvacuum deposition, vapor deposition and liquid coating. Exemplarydeposition methods include physical vapor deposition (PVD), chemicalvapor deposition (CVD), sublimation or liquid coating methods. Suchmethods form part of the general knowledge in the field and are wellknown to the skilled person.

Before the SAM treatment, i.e. the formation of the self-assembledmonolayer, the metal or metal oxide surface is preferably subjected to awashing step. A preferred washing step comprises an acidic washing witha acid or a blend of acids, said acids being organic or inorganic acids.Examples of suitable acids are acetic acid, citric acid or hydrochloricacid. Alternatively the metal or metal oxide surface may be subjected toa plasma treatment step.

In a preferred embodiment, the washing step and the SAM treatment arecombined into a single step. For example, this combined step may becarried out by applying a formulation in accordance with the presentinvention to the metal or metal oxide surface, said formulationcomprising a precursor compound as defined above and an acid as definedabove.

Alternatively the washing step and the SAM treatment may be carried outsequentially in two separate steps.

The soaking time, i.e. the time during which the formulation is appliedto the metal or metal oxide surface, is preferably at least 5 s and atmost 72 h.

In the preparation of the other layers of the electronic devices,preferably the organic electronic devices, of the present inventionstandard methods may be used to deposit the various layers and materialsas described above.

Preferably the deposition of individual functional layers in thepreparation of the present electronic devices, such as for example theorganic semiconducting layer or the insulator layer, is carried outusing solution processing techniques. This can be done for example byapplying a formulation, preferably a solution, comprising the organicsemiconducting material or the dielectric material and furthercomprising one or more organic solvents, onto the previously depositedlayer, followed by evaporation of the solvent(s). Preferred depositiontechniques include, without limitation, dip coating, spin coating, inkjet printing, letter-press printing, screen printing, doctor bladecoating, roller printing, reverse-roller printing, offset lithographyprinting, flexographic printing, web printing, spray coating, brushcoating, or pad printing. Very preferred solution deposition techniquesare spin coating, flexographic printing and inkjet printing.

In an OFET device according to the present invention, the dielectricmaterial for the gate insulator layer is preferably an organic material.It is preferred that the dielectric layer is solution coated whichallows ambient processing, but could also be deposited by various vacuumdeposition techniques. When the dielectric is being patterned, it mayperform the function of interlayer insulation or act as gate insulatorfor an OFET. Preferred deposition techniques include, withoutlimitation, dip coating, spin coating, ink jet printing, letter-pressprinting, screen printing, doctor blade coating, roller printing,reverse-roller printing, offset lithography printing, flexographicprinting, web printing, spray coating, brush coating or pad printing.Ink-jet printing is particularly preferred as it allows high resolutionlayers and devices to be prepared. Optionally, the dielectric materialcould be cross-linked or cured to achieve better resistance to solventsand/or structural integrity and/or to improve patterning(photolithography). Preferred gate insulators are those that provide alow permittivity interface to the organic semiconductor.

Suitable solvents are selected from solvents including but not limitedto hydrocarbon solvents, aromatic solvents, cycloaliphatic cyclicethers, cyclic ethers, acetates, esters, lactones, ketones, amides,cyclic carbonates or multi-component mixtures of the above. Examples ofpreferred solvents include cyclohexanone, mesitylene, xylene,2-heptanone, toluene, tetrahydrofuran, MEK (methyl ethyl ketone), MAK(2-heptanone), cyclohexanone, 4-methylanisole, butyl-phenyl ether andcyclohexylbenzene, very preferably MAK, butyl phenyl ether orcyclohexylbenzene.

The total concentration of the respective functional material (organicsemiconducting material or gate dielectric material) in the formulationis preferably from 0.1 to 30 wt %, preferably from 0.1 to 5 wt %,relative to the total weight of the formulation (i.e. functionalmaterial(s) and solvent(s)). In particular organic ketone solvents witha high boiling point are advantageous for use in solutions for inkjetand flexographic printing.

When spin coating is used as deposition method, the OSC or dielectricmaterial is spun for example between 1000 and 2000 rpm for a period offor example 30 seconds to give a layer with a typical layer thicknessbetween 0.5 and 1.5 μm. After spin coating the film can be heated at anelevated temperature to remove all residual volatile solvents.

Optionally the dielectric material layer is annealed after exposure toradiation, for example at a temperature from 70° C. to 130° C., forexample for a period of from 1 to 30 minutes, preferably from 1 to 10minutes. The annealing step at elevated temperature can be used tocomplete the cross-linking reaction that was induced by the exposure ofthe cross-linkable groups of the dielectric material to photoradiation.

All process steps described above and below can be carried out usingknown techniques and standard equipment which are described in prior artand are well-known to the skilled person. For example, in thephotoirradiation step a commercially available UV lamp and photomask canbe used, and the annealing step can be carried out in an oven or on ahot plate.

The thickness of a functional layer (organic semiconducting layer ordielectric layer) in an electronic device according to the presentinvention is preferably from 1 nm (in case of a monolayer) to 10 μm,very preferably from 1 nm to 1 μm, most preferably from 5 nm to 500 nm.

Various substrates may be used for the fabrication of organic electronicdevices, for example silicon wafers, glass or plastics, plasticsmaterials being preferred, examples including alkyd resins, allylesters, benzocyclobutenes, butadiene-styrene, cellulose, celluloseacetate, epoxide, epoxy polymers, ethylene-chlorotrifluoro ethylene,ethylene-tetra-fluoroethylene, fibre glass enhanced plastic,fluorocarbon polymers, hexafluoropropylenevinylidene-fluoride copolymer,high density polyethylene, parylene, polyamide, polyimide, polyaramid,polydimethylsiloxane, polyethersulphone, poly-ethylene,polyethylenenaphthalate, polyethyleneterephthalate, polyketone,polymethylmethacrylate, polypropylene, polystyrene, polysulphone,polytetrafluoroethylene, polyurethanes, polyvinylchloride, siliconerubbers, and silicones.

Preferred substrate materials are polyethyleneterephthalate, polyimide,and polyethylenenaphthalate. The substrate may be any plastic material,metal or glass coated with the above materials. The substrate shouldpreferably be homogeneous to ensure good pattern definition. Thesubstrate may also be uniformly pre-aligned by extruding, stretching,rubbing or by photochemical techniques to induce the orientation of theorganic semiconductor in order to enhance carrier mobility.

A preferred process for the manufacture of organic electronic devices inaccordance with the present invention comprises the steps of

-   (a) depositing a metal or a metal oxide to form a source electrode    and a drain electrode on a substrate,-   (b) optionally washing the surfaces of said source electrode and    said drain electrode; and-   (c) applying one or more precursor compounds of formula (I′) or (I″)    as defined above to said source electrode and said drain electrode,    thus obtaining a self-assembled monolayer on the surfaces of said    source electrode and said drain electrode;-   (d) depositing a organic semiconducting material onto the source and    drain electrodes and the self-assembled monolayer, thus forming an    organic semiconducting layer.

Optionally steps (b) and (c) may be combined into a single step.

Optionally in step (c) the application of the one or more precursorcompounds as defined above may be followed by at least partial removalof any solvents present or by annealing the self-assembled monolayer orby both.

Optionally in step (d) the deposition of the organic semiconductingmaterial may be followed by at least partial removal of any solventspresent or by annealing the organic semiconducting material or by both.

In addition to above steps (a) to (d) the process for manufacturing theorganic electronic devices in accordance with the present invention mayfurther comprise the following steps:

-   (e) depositing a gate insulator material onto said organic    semiconducting layer, thereby forming a gate insulator layer;-   (f) depositing a gate electrode onto said gate insulator layer; and-   (g) optionally depositing a passivation layer onto said gate    electrode.

For the preparation of a top gate transistor, the source and drainelectrodes are usually applied onto a substrate as defined above,followed by the deposition thereon of a self-assembled monolayer inaccordance with the present invention.

A gate insulator can then be applied on the organic semiconductinglayer, onto which in turn a gate electrode may be deposited.

For the preparation of a bottom gate transistor, the gate electrode isusually applied to a substrate. The gate insulator layer is then formedon top of said gate electrode. Source and drain electrodes are thenapplied to the gate insulator, followed by the deposition thereon of aself-assembled monolayer in accordance with the present invention.

Depending upon the type of electronic device to be manufactured and therespective architecture, the above process for manufacturing organicelectronic devices may be modified, for example by including theformation of additional layers, which are different from the onesincluded in any of above steps (a) to (g).

Process conditions may also be adapted without difficulty to takeaccount of the nature of the specific materials used in the productionof the desired electronic device.

Unless the context clearly indicates otherwise, as used herein pluralforms of the terms herein are to be construed as including the singularform and vice versa.

Throughout the description and claims of this specification, the words“comprise” and “contain” and variations of the words, for example“comprising” and “comprises”, mean “including but not limited to”, andare not intended to (and do not) exclude other components.

It will be appreciated that variations to the foregoing embodiments ofthe invention can be made while still falling within the scope of theinvention. Each feature disclosed in this specification, unless statedotherwise, may be replaced by alternative features serving the same,equivalent or similar purpose. Thus, unless stated otherwise, eachfeature disclosed is one example only of a generic series of equivalentor similar features.

All of the features disclosed in this specification may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. In particular, thepreferred features of the invention are applicable to all aspects of theinvention and may be used in any combination. Likewise, featuresdescribed in non-essential combinations may be used separately (not incombination).

Above and below, unless stated otherwise percentages are percent byweight and temperatures are given in degrees Celsius. The values of thedielectric constant E (“permittivity”) refer to values taken at 20° C.and 1,000 Hz.

EXAMPLES

The advantages of the present invention are further illustrated by thefollowing non-limiting examples.

If not otherwise indicated starting materials were purchased throughcommercial sources, such as for example Aldrich Chemicals.

Example 1 Synthesis of TMP-SH Step a

3,4,5-Trimethoxyaniline 1 (916 mg, 5.00 mmol, 1.00 eq) was dissolved in10 ml methanol, and 10 vol % hydrochloric acid was added. The mixturewas cooled to 0° C. Over a period of 30 minutes a solution of sodiumnitrite (517 mg, 7.50 mmol, 1.50 eq) in 20 ml water was added drop wise.The mixture was stirred for an additional 15 minutes at 0° C. whereuponit turned to a brownish color. The solution (still at 0° C.) was pouredinto a preheated (65° C.) solution of potassium ethyl xanthate (1.60 g,10.0 mmol, 2.00 eq) in water (30 ml). Formation of gas could be observedas well as a change of color to yellow. The mixture was stirred for anadditional 15 minutes at 65° C. and then allowed to cool to roomtemperature. The reaction mixture was extracted with ethyl acetate. Thecombined organic extracts were washed with brine, dried over sodiumsulfate and concentrated under vacuum. The residue was purified by flashcolumn chromatography (silica gel; mixture of petrol ether and ethylacetate in 10:1 ratio). 611 mg (42%) of the pure product 2 could beobtained as orange-yellow solid.

¹H-NMR (300 MHz; CDCl₃; MJ024): 6.73 (s, 2H); 4.62 (q, ³J_(H-H)=7.1 Hz,2H); 3.88 (s, 3H); 3.85 (s, 6H); 1.34 (t, ³J_(H-H)=7.1 Hz, 3H).

Step b

3,4,5-Trimethoxyphenyl ethyl xanthate 2 (611 mg, 2.12 mmol, 1.00 eq) wasdissolved in 10 ml of degassed (nitrogen flow; ca. 1.5 h) ethanol. 8 mlof a degassed, aqueous 3 mmol/l sodium hydroxide solution was added andthe solution was heated to 65° C. for 2 hours. During the heating theformation of a precipitate, closely followed by its renewed dissolution,could be observed. The solution was cooled to room temperature andacidified using 10% aqueous hydrochloric acid (pH=5). The acidifiedreaction mixture was extracted with ethyl acetate. The combined organicextracts were washed with brine, dried over sodium sulfate andconcentrated under vacuum. The residue was purified by flash columnchromatography (silica gel; mixture of petrol ether and ethyl acetate ina 10:1 ratio). Upon thorough drying under vacuum 346 mg (82%) of yellowcrystalline solid 3 was obtained.

¹H-NMR (300 MHz; CDCl₃; MJ027): 6.53 (s, 2H); 3.84 (s, 6H); 3.81 (s,3H); 3.47 (bs, 1H).

EI-MS (MJ027): m/z=200.0 (Molecule; C₉H₁₂O₃S. calculated 200.1).

-   -   185.0 (Fragment 1 (molecule—CH₃); C₉H₁₂O₃S.        -   calculated: 185.0).

Example 2 Synthesis of TMP-CH₂—SH

The synthesis was carried out in analogy to C. Märcher, Ann. Chem.Pharm. 1865, 136, 75. Sodium hydrosulfide (1.852 g; 25.0 mmol; 5.0 eq)was dissolved in 25 ml of ethanol. The solution was purged withnitrogen. 3,4,5-Trimethoxybenzyl-chloride (1.083 g; 5.00 mmol; 1.0 eq)was dissolved in 25 ml of ethanol and added dropwise to the previouslyprepared solution over a period of 15 minutes. Upon completion of theaddition TLC-analysis showed that the reaction was complete. The mixturewas diluted with water and extracted with ethyl acetate. The combinedorganic layers were washed with brine, dried over Na₂SO₄ andconcentrated in vacuo. The crude product was purified via flash columnchromatography (SiO₂, mixture of petroleum ether and ethyl acetate in5:1 ratio). 0.236 g of product 5 could be obtained as a colourless,wax-like solid (22% yield).

¹H-NMR (300 MHz, CDCl₃, MJ073): 6.55 (s, 2H); 3.87 (s, 6H); 3.83 (s,3H); 3.70 (d, 3JH-H=7.5 Hz, 2H); 1.80 (t; 3JH-H=7.5 Hz; 1H)

Example 3 Transistor Fabrication and Performance Measurement

Bottom contact-top gate transistors having a channel width of 50 μm anda channel length of 1000 μm (see FIG. 3 for a schematic representation)were prepared on glass substrates. Ag electrodes were deposited onto theglass substrates by thermal evaporation, using lateral structuring witha shadow mask. The resulting structures was then immersed in a 1 mmol/lsolution of either TMP-SH 3 or TMP-CH₂—SH 5 in chlorobenzene.Subsequently a n-type semiconductor (ActivInk™ N2200 [P(NDI2OD-T2)]),Polyera Corporation, Skokie, Ill., USA) was spin-coated thereon from a 1wt % chlorobenzene solution and annealed at 100° C. for 180 s. Then adielectric layer was formed by spin coating an amorphous fluoropolymer(CYTOP™, ASAHI GLASS COMPANY) and annealed at 100° C. for 300 s. Allspin coating steps were performed under nitrogen atmosphere in aglovebox. Finally a Ag gate electrode was deposited by thermalevaporation onto the dielectric layer.

Thicknesses of the respective layers were determined with a Dektakprofilometer with the following results:

TABLE 1 Thickness [nm] Ag source and drain electrodes 50 ± 5Semiconductor layer (ActivInk ™ N2200) 650 ± 50 Dielectric layer(CYTOP ™) 80 ± 5

Transistor transfer and output measurements were conducted in ambientatmosphere using an Agilent parameter analyzer. Transfer characteristicsare shown in FIG. 4. Table 2 shows the respective mobilities, ratiobetween on- and off-current, the threshold voltage as well as the timefor which the Ag-source and drain electrodes were immersed in thesolution of TMP-SH and TMP-CH₂—SH, respectively.

TABLE 2 Self-assembled monolayer Precursor No SAM TMP-SH TMP-CH₂-SHcompound (comparative) (Ex. 1) (Ex. 2) μ_(SAT) [cm²/Vs] 0.01 0.08 0.08 Ion/off 5.6 · 10³ 7.6 · 10⁴ 6 · 10⁴ V_(Threshold) [V] 60.1 42.4 64.3Immersion time [h] 0 24 24

The results clearly show the advantages of the present invention. Incomparison to the devices comprising the untreated Ag source and drainelectrodes the devices comprising the present self-assembled monolayersurprisingly show very much improved properties, namely increasedcurrents at a given voltage. In addition the devices in accordance withthe present invention also show an improved ratio between on-current andoff-current.

Example 4 Work Function and Contact Angle

To quantify the efficiency of the moieties of the present invention therespective work function (WF) of an Au surface and the contact angle ofthe precursor compound of Example 2 (TMP-CH₂—SH) was tested incomparison to precursor compounds benzylthiol (C₆H₅—CH₂—SH) and4-methoxy-a-toluenethiol. The results are given in Table 3.

TABLE 3 WF Shift in WF Contact angle Precursor Compound [eV] [meV](water) Benzylthiol 4.20 −500 90° 4-methoxy-α-toluenethiol 4.20 −500 75°TMP-CH₂-SH 4.50 −250 65°

It is shown that TMP-CH₂—SH, a precursor compound in accordance with thepresent invention, shifts the work function but at the same time has asignificant higher impact on the contact angle than the comparativecompounds. TMP-CH₂—SH therefore allows a different balance betweenelectronic properties and wettability. Based on these data it isexpected that the precursor compounds of the present invention willallow for a much wider choice in solvents in the preparation ofelectronic devices. In consequence it is expected that the preparationof electronic devices will be facilitated as the solvents that may beused may be less destructive on already formed layers of the electronicdevice.

Example 5 Transistor Fabrication and Performance Measurement

Bottom contact-top gate transistors having a channel width of 50 μm anda channel length of 1000 μm (see FIG. 3 for a schematic representation)were prepared on glass substrates, which had been cleaned with acetoneand isopropanol in an ultrasonic bath. Au electrodes were deposited ontothe glass substrates by thermal evaporation using a shadow mask. Theresulting structures were then immersed for 1000 s in a 0.1 mmol/lsolution of either TMP-SH 3 or TMP-CH₂—SH 5 in chlorobenzene.Subsequently, in a glovebox under nitrogen atmosphere a n-typesemiconductor (ActivInk™ N2200 [P(NDI2OD-T2)]), Polyera Corporation,Skokie, Ill., USA) was spin-coated thereon from a 10 mg/ml chlorobenzenesolution and heated on a hot plate at 100° C. for 180 s. Then adielectric layer of Parylene N was formed by vapor phase depositionusing a PDS2010 Coating System by SPS™. Finally a ca. 100 nm thick Aggate electrode was deposited by thermal evaporation onto the dielectriclayer using a shadow mask. The resulting devices could be used as suchunder ambient conditions without any further encapsulation layer.

Thicknesses of the respective layers were determined with a Dektakprofilometer with the following results:

TABLE 4 Thickness [nm] Au source and drain electrodes ca. 60Semiconductor layer (ActivInk ™ N2200) 80 ± 5 Dielectric layer(Parylene-N) 270 ± 10

Transistor transfer and output measurements were conducted in ambientatmosphere using an Agilent parameter analyzer with a source-drainvoltage of 15 V. Transfer characteristics are shown in FIG. 5. Table 5gives the respective contact resistances, channel resistances andthreshold voltages.

TABLE 5 Self-assembled monolayer Precursor No SAM TMP-SH TMP-CH₂-SHcompound (comparative) (Ex. 1) (Ex. 2) Contact [Ω cm] 5.2 · 10⁶ 1.5 ·10⁴ 4.8 · 10⁴ resistance Channel [Ω cm⁻¹] 7.5 · 10⁹ 8.9 · 10⁸ 1.7 · 10⁹resistance V_(Threshold) [V] 18.4 4.9 6.4

The results clearly show the advantages of the present invention. Incomparison to the devices comprising the untreated Au source and drainelectrodes the devices comprising the present self-assembled monolayersurprisingly show very much improved properties, namely increasedcurrents at a given voltage (see FIG. 5). The positive effect of thepresence of a self-assembled monolayer in accordance with the presentapplication can also clearly be seen in the improvement in resistances,be it contact resistance as well as channel resistance. It is also notedthat the threshold voltages are strongly shifted in the direction of 0.

1. Self-assembled monolayer comprising a moiety of formula (I)

wherein R¹ is selected from the group consisting of methyl, ethyl,methyl wherein one or more hydrogen is substituted by fluorine and ethylwherein one or more hydrogen is substituted by fluorine; R² is —CH₂— or—CF₂—; Ar¹ is para-phenylene or a para-phenylene wherein one or morecarbon ring atom is substituted by N; X¹ is selected from the groupconsisting of —X^(a)—, —X^(a)—X^(b)—, —C(═X^(a))—X^(b)—, —X^(a)O₃—,—X^(a)—X^(b)O₃—, —PO₂H— and —PO₃H—, with X^(a) and X^(b) beingindependently of each S or Se; a is 2, 3, 4 or 5; b is 0, 1 or 2; c is0, 1 or 2; d is 0, 1 or 2; and e is 0, 1 or
 2. 2. Self-assembledmonolayer comprising the moiety according to claim 1, wherein R¹ ismethyl.
 3. Self-assembled monolayer comprising the moiety according toclaim 1, wherein R² is —CH₂—.
 4. Self-assembled monolayer comprising themoiety according to claim 1, wherein Ar¹ is selected from the groupconsisting of the following formulae (II-1) to (II-7):


5. Self-assembled monolayer comprising the moiety according to claim 1,wherein X¹ is selected from the group consisting of —S—, —S—S—,—C(═S)—S—, —SO₃—, —S—SO₃—, —PO₂H— and —PO₃H—.
 6. Self-assembledmonolayer comprising the moiety according to claim 1, wherein is —S—. 7.Self-assembled monolayer comprising the moiety according to claim 1,wherein a is
 3. 8. Self-assembled monolayer comprising the moietyaccording to claim 1, wherein b+c+d+e+≧1.
 9. Self-assembled monolayercomprising the moiety according to claim 1, wherein e is
 1. 10.Self-assembled monolayer comprising the moiety according to claim 1,wherein b is 1, c is 1, d is 0, and e is 0 or 1; or wherein b is 0, c is1, d is 0, and e is 0 or
 1. 11. Organic electronic device comprising theself-assembled monolayer of claim
 1. 12. Organic electronic deviceaccording to claim 11, wherein the organic electronic device is selectedfrom the group consisting of organic field effect transistors (OFET),thin film transistors (TFT), integrated circuits (IC), logic circuits,capacitors, radio frequency identification (RFID) tags, devices orcomponents, organic light emitting diodes (OLED), organic light emittingtransistors (OLET), flat panel displays, backlights of displays, organicphotovoltaic devices (OPV), organic solar cells (OSC), photodiodes,laser diodes, photoconductors, organic photodetectors (OPD),electrophotographic devices, electrophotographic recording devices,organic memory devices, sensor devices, charge injection layers, chargetransport layers or interlayers in polymer light emitting diodes(PLEDs), Schottky diodes, planarising layers, antistatic films, polymerelectrolyte membranes (PEM), conducting substrates, conducting patterns,electrode materials in batteries, alignment layers, biosensors,biochips, security markings, security devices, and components or devicesfor detecting and discriminating DNA sequences.
 13. Process for thepreparation of the self-assembled monolayer of claim 1, said processcomprising the steps of (a) providing a metal surface or a metal oxidesurface, and (c) applying one or more precursor compound to said metalsurface or metal oxide surface, thus obtaining a self-assembledmonolayer on said metal surface or metal oxide surface, wherein theprecursor compound comprises a moiety of formula (I)

wherein R¹ is selected from the group consisting of methyl, ethyl,methyl wherein one or more hydrogen is substituted by fluorine and ethylwherein one or more hydrogen is substituted by fluorine; R² is —CH₂— or—CF₂—; Ar¹ is para-phenylene or a para-phenylene wherein one or morecarbon ring atom is substituted by N; X¹ is selected from the groupconsisting of —X^(a)—, —X^(a)—X^(b)—, —C(═X^(a))—X^(b)—, —X^(a)O₃H,—X^(a)—X^(b)O₃H, —PO₂H₂ and —PO₃H₂, with X^(a) and X^(b) beingindependently of each S or Se; a is 2, 3, 4 or 5; b is 0, 1 or 2; c is0, 1 or 2; d is 0, 1 or 2; and e is 0, 1 or
 2. 14. Process according toclaim 13, wherein the precursor compound is of formula (I′) or (I″)


15. The process according to claim 13, wherein R¹ is methyl.
 16. Theprocess according to claim 13, wherein R² is —CH₂—.
 17. The processaccording to claim 13, wherein Ar¹ is selected from the group consistingof the following formulae (II-1) to (II-7):


18. The process according to claim 13, wherein X¹ is selected from thegroup consisting of —S—, —S—S—, —C(═S)—S—, —SO₃—, —S—SO₃—, —PO₂H— and—PO₃H—.
 19. The process according to claim 13, wherein X¹ is —S—. 20.The process according to claim 13, wherein a is 3.